Robert Downey Jr. took to social media on Wednesday to share a behind-the-scenes photo from the set of Avengers: Infinity War. In it, he poses with Benedict Cumberbatch, Mark Ruffalo, and Benedict Wong.

However, more revealing than the characters of Doctor Strange, Iron Man, the Hulk, and Wong coming together on set is a detail spotted deeper in the photo. Sitting together in costume, Downey Jr. is sporting a shirt with a certain circular hole in the chest area.

Fans of the Marvel Cinematic Universe realzie Tony Stark had his arc reactor removed from his chest by the end of Iron Man 3. So, why does he have the reactor in his chest again in the photo below?

There are several go-to theories regarding the arc reactor resurfacing.

The first is that Tony has never fought an enemy such as Thanos, nor have any of the other Avengers. The villain will be the most formidable foe they have ever come across (with the exception of Strange’s encounter with Dormammu). Tony might experience a change of heart, literally, regarding his suits in Spider-Man: Homecoming or early events of Avengers: Infinity War which lead to him needing a bit more power to take on the villain.

Then, there is the more farfetched possibility of Doctor Strange’s Eye of Agamotto being taken from him by the Mad Titan. Such a move seems inevitable but the next part is where it gets a little less likely: Thanos sends the heroes to a point in time where Stark was relying on the arc reactor to keep himself alive.

Then, of course, there is the possible connection to needing the arc reactor and going to the cosmos. Tony only scratched the surface of taking his suit to space when he diverted a nuclear missile from New York City through a wormhole into space. His suit promptly shut down so, clearly, there is room for improvement.

For one reason or another, Tony Stark will be sporting an arc reactor in Avengers: Infinity War.

UP NEXT: Spider-Man: Homecoming Sequel Will Feature Different Marvel Studios Hero

As the Avengers and their allies have continued to protect the world from threats too large for any one hero to handle, a new danger has emerged from the cosmic shadows: Thanos. A despot of intergalactic infamy, his goal is to collect all six Infinity Stones, artifacts of unimaginable power, and use them to inflict his twisted will on all of reality. Everything the Avengers have fought for has led up to this moment – the fate of Earth and existence itself has never been more uncertain.”

Avengers: Infinity War is described by Marvel Studios as the culmination of everything in the Marvel Cinematic Universe since Iron Man in 2008. The movie is filming now under directors Anthony and Joe Russo, from a screenplay by Christopher Markus and Stephen McFeely.

The expansive confirmed cast includes Robert Downey, Jr., Chris Evans, Chris Hemsworth, Mark Ruffalo, Jeremy Renner, Scarlett Johansson, Tom Holland, Elizabeth Olsen, Paul Bethany, Sebastian Stan, Benedict Cumberbatch, Benedict Wong, Chris Pratt, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Bradley Cooper, Pom Klementieff, and Josh Brolin as the villain Thanos. Avengers: Infinity War and its as-yet-untitled sequel are filming back-to-back for a May 4, 2018 and May 3, 2019 release, respectively.

More Avengers: Infinity War News: Chris Hemsworth Hints At The MCU’s Final Infinity Stone / Avengers Infinity War: 5 Marvel Infinity Saga Easter Eggs Fans Want / Benedict Wong Fanboys Out About Delivering Infinity Stone Line & Joining Avengers: Infinity War / Russo Brothers Confirm Next Two Avengers Movies Still Directly Connected

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